[KCM] Show the same name in the replication model that's shown in the title

Summary:
This patch makes the name shown in the combobox match the name shown for each individual
output. Now they match, so you can actually tell what output is being replicated.

Targeting the 5.17 branch.

Test Plan:
Before: {F7608190}
After: {F7608191}

Reviewers: romangg, #vdg

Reviewed By: romangg

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24704